This invention relates to the vapor phase production of aliphatic alcohols by heterogeneous catalysis. More particularly, it relates to a novel solid catalyst composition and the process for using the catalyst to convert methanol and ethanol in the vapor phase to higher linear primary alcohols.
Numerous attempts have been made in the past to develop a commercially viable process for converting readily available lower alcohols to more valuable higher linear primary alcohols which are presently in great demand as commodity chemicals.
These efforts were generally directed at developing the so-called Guerbet synthesis, a heterogeneous catalysis reaction whereby a primary or secondary alcohol containing a methylene group alpha to the carbinol moiety is condensed with itself or with a different alcohol likewise containing the aforesaid methylene group to form a higher alcohol containing twice the number of carbon atoms of the single starting alcohol, or, in the case of mixed starting alcohols, the sum of the number of carbon atoms in each reacting pair of alcohols. For example, ethanol can be self-condensed to form n-butanol while a mixture of ethanol and n-propanol can be condensed to form n-butanol, 2-methylpentanol, n-pentanol, and 2-methylbutanol.
Heretofore, much of the development work or improving the Guerbet reaction has been centered on the nature of the catalyst system. Thus, in U.S. Pat. No. 2,762,847, there is disclosed the use of catalysts composed of alkali or alkaline earth metal phosphates, particularly ortho- and pyrophosphates. U.S. Pat. No. 2,971,033 discloses the use of a mixture of potassium carbonate, magnesium oxide and copper chromite to effect the Guerbet reaction, while U.S. Pat. No. 3,479,412 teaches that the conversion will proceed in the presence of catalysts made up of soluble compounds of metals of the platinum series (e.g., rhodium, palladium) and ligands selected from the group consisting of organic compounds of trivalent phosphorus, arsenic and antimony.
A somewhat different method than the Guerbet synthesis for making higher alcohols is the so-called oxo reaction or hydroformylation of olefins whereby carbon monoxide and hydrogen are added across the double bond in the pressure of a catalyst to form the alcohol functionality. Typical of catalyst systems which are useful in this approach to higher alcohols are those described in U.S. Pat. No. 3,239,570 which suggests that metals of Group VII B (e.g., manganese) or Group VIII (e.g., rhodium) of the Periodic Table of the Elements can be complexed with carbon monoxide and a tertiary organic arsine to give a catalyst which effects the desired transformations. For a more generalized treatment of the oxo synthesis as applied to the preparation of higher alcohols, see P. H. Emmett, ed., Catalysis, vol. V, pages 73-130 (Reinhold, New York 1957).
In yet another technique for synthesizing higher alcohols from lower ones, U.S. Pat. No. 3,387,043 teaches that Cn alcohols can be made from Cn-1 alcohols by homologation using hydrogen and carbon monoxide in the presence of soluble cobalt compounds as catalyst.
Notwithstanding the variety and extent of previous investigations into the synthesis of alcohols from lower alcohols and olefins, there has heretofore been no commercially successful procedure for the one-step conversion of such simple and cheap starting materials as methanol and ethanol into more valuable products such as n-propanol and n-butanol. Chief among the reasons for this has been the failure of previous heterogeneous catalyst formulations to withstand the elevated temperatures and pressures inherent in these processes without loss of catalyst activity in a short period of time. For example, it is known that so-called methanol synthesis catalysts such as the potassium carbonate-doped CuO/ZnO system are effective in converting carbon monoxide and hydrogen to methanol. However, when these catalysts are applied to the synthesis of higher alcohols, they invariably undergo rapid ageing with consequent loss in catalytic activity and selectivity to linear primary alcohols. As a result, these catalysts, when applied to the conversion of, say, methanol and ethanol to higher alcohols, usually have an effective life of but a few hours, which is too short to justify their employment in commercial continuous processes. For a general discussion of the use of methanol synthesis catalysts to make higher n-alcohols and the problems associated therewith, see U.S. Pat. No. 1,770,165, U.S. Pat. No. 1,910,582, and P. H. Emmet, ed., Catalysis, vol. V, pages 131-174 (1957).
A long felt need has therefore existed in chemical industry for a catalyst system and a process for using same to facilitate the conversion of relatively cheap starting materials, such as methanol and ethanol, to more valuable product alcohols of the linear primary type without degrading the activity or selectivity of the catalyst even after prolonged continuous use at elevated temperature and pressure.
Accordingly, it is an object of the invention to provide a catalyst system for the conversion of lower alcohols selectively to higher, linear primary alcohols which possesses a high degree of longevity and resistance to degradation in catalytic activity and selectivity.
Another object is to provide an improved process for the selective conversion of lower alcohols to higher, linear primary alcohols under conditions of hetergeneous catalysis which can be operated continuously for extended periods of time without substantial degradation in catalyst activity or selectivity.
These and other objects of the invention, as well as a fuller understanding of the advantages thereof can be had by reference to the following detailed description and claims.